This is WEEKEND EDITION from NPR News. I'm Scott Simon. A federal judge in Arizona has ruled against the man who calls himself America's toughest sheriff. The judge ruled that the Maricopa County Sheriff's Department has used racial profiling to enforce the state's tough immigration laws. Sheriff Joe Arpaio has maintained that his department has the authority to round up undocumented immigrants. NPR's Ted Robbins has been following the case and joins us now. Ted, thanks for being with us.

TED ROBBINS, BYLINE: You're welcome.

SIMON: And why this ruling now?

ROBBINS: Well, Scott, Sheriff Arpaio has been holding what he calls saturation patrols in Phoenix-area neighborhoods. They're aimed at rounding up people in the country without proper documents. Deputies have been stopping cars and detaining people while they ran immigration status checks through the federal government's database. So, the case was brought by a group of citizens and legal residents who said they'd been stopped just because they are Hispanic. Federal judge Murray Snow heard the case in a weeklong trial last summer and we've been waiting for this ruling ever since. The judge ruled that the sheriff used illegal racial profiling in his stops and in his raids on businesses, that he'd stopped these people just because their skin was brown. The Justice Department also took legal action against Sheriff Arpaio in a different case. But this is the first time that a judge has ruled that the tactics are illegal, then the judge said the practice has to stop immediately.

SIMON: And, of course, this would be considered a big victory for the people who filed the lawsuit.

ROBBINS: They're obviously delighted. We spoke with a couple of people. Why don't we hear from Cecilia Wang of the ACLU Immigrant Rights Project? She was one of the attorneys on the case.

CECILIA WANG: Latino residents of Maricopa County have been really terrorized and oppressed by the sheriff's policy targeting Latino residents for traffic stops, regardless of your immigration status.

LYDIA GUZMAN: We're hoping that the sheriff takes this to heart and involves the community in this.

SIMON: Any response yet from Sheriff Arpaio or anyone in the department?

ROBBINS: Not yet. The sheriff has never indicated that he would back down before, though, so it'd be surprising if he did now - at least verbally. Listeners may remember that he's the guy who started the tent jails in Phoenix and forced inmates to wear pink underwear. His tough attitude, period, much less his tough attitude on immigration, is one of the things that seem to have gotten him re-elected time and again, including last November.

SIMON: Ted, I gather that the judge left open of how the ruling can be enforced. How do you enforce a ruling against the person who is supposed to enforce the law?

ROBBINS: Right. Now, the sheriff can appeal the case - we should say that first. But, right, since the ruling's effective immediately, it's a really important point, Scott. The judge has ordered Arpaio to stop the immigration tactics. But, like you said, he's a law enforcement officer, so who's there to ensure he's complying? The plaintiff's say they're going to go back to court to ask the judge to enforce his ruling maybe with a monitor appointed by the courts. And that's what the Department of Justice asked for in a different case against the sheriff. Judge Snow has indicated that he might be open to that. DHS has already stripped the sheriff of his authority to use federal resources to enforce immigration law.

SIMON: Does this ruling have any potential significance beyond Maricopa County?

ROBBINS: You know, that's a tough question because nobody has been challenge beyond Maricopa County. He is the only one in the state of Arizona, for instance, to enforce a state law against smuggling human beings. No other state has that law, and that's the law that he was using to defend his practices.

SIMON: NPR's Ted Robbins speaking with us from Tucson. Thanks very much for being with us, Ted.